Methods of graphene growth and related structures

ABSTRACT

A method and structure for providing uniform, large-area graphene by way of a transfer-free, direct-growth process. In some embodiments, a SAM is used as a carbon source for direct graphene synthesis on a substrate. For example, a SAM is formed on an insulating surface, and a metal layer is formed over the SAM. The metal layer may serve as a catalytic metal, whereby the SAM is converted to graphene following an annealing process. The SAM is deposited using a VPD process (e.g., an ALD process and/or an MLD process). In some embodiments, a CNT having a controlled diameter may be formed on the surface of a nanorod by appropriately tuning the geometry of the nanorod. Additionally, in some embodiments, a curved graphene transistor may be formed over a curved oxide surface, thereby providing a band gap in a channel region of the graphene transistor.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. patent applicationSer. No. 15/925,195, filed Mar. 19, 2018, which is a divisionalapplication of U.S. patent application Ser. No. 15/169,557, filed May31, 2016, the disclosures of which are incorporated by reference hereinin their entirety.

BACKGROUND

The electronics industry has experienced an ever increasing demand forsmaller and faster electronic devices which are simultaneously able tosupport a greater number of increasingly complex and sophisticatedfunctions. Accordingly, there is a continuing trend in the semiconductorindustry to manufacture low-cost, high-performance, and low-powerintegrated circuits (ICs). Thus far these goals have been achieved inlarge part by scaling down semiconductor IC dimensions (e.g., minimumfeature size) and thereby improving production efficiency and loweringassociated costs. However, such scaling has also introduced increasedcomplexity to the semiconductor manufacturing process. Thus, therealization of continued advances in semiconductor ICs and devices callsfor similar advances in semiconductor manufacturing processes andtechnology.

Graphene, a two-dimensional (2-D) sheet of carbon atoms bonded to oneanother in a hexagonal crystal lattice, has recently been introduced asa potential replacement channel material for transistor devices. Inaddition to its high intrinsic mobility, graphene has attracted greatinterest for its other unique properties such as large currentdensities, thermodynamic and mechanical stability, and high saturationvelocity, among others. Graphene films have often been obtained bymechanical exfoliation (e.g., from a bulk graphite source), butmechanical exfoliation results in graphene films that are small (e.g.,tens of microns) and non-scalable. Large-area graphene films have beenproduced by methods such as epitaxial growth on silicon carbide (SiC)substrates and chemical vapor deposition (CVD)-growth (e.g., involvingthe catalyzed decomposition of hydrocarbons on a metal surface), butsuch methods also have drawbacks (e.g., high-cost of SiC substrates andhigh processing temperature for SiC epitaxial growth). Regardless of thetechnique used for producing graphene films, the fabrication ofgraphene-based devices generally involves transfer of a graphene layer(e.g., from a growth substrate or from the bulk graphite source), andonto a target substrate upon which the graphene-based device will befabricated. As a result of the transfer process, grain boundaries, pointdefects, wrinkles, folds, tears, cracks, impurities, or other defectsmay be introduced into the transferred graphene layer and therebydetrimentally affect the properties of any subsequently fabricateddevices. Thus, existing techniques have not proved entirely satisfactoryin all respects.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a cross-sectional view of a back-gated graphene device;

FIG. 2 is a flow chart of a method of fabricating a graphene deviceaccording to one or more aspects of the present disclosure;

FIGS. 3, 4, 5, 6, 7, and 8 illustrate cross sectional views ofembodiments of a graphene device according to one or more aspects of thepresent disclosure and corresponding to one or more steps of the methodof FIG. 2;

FIGS. 4A, 4B, and 4C illustrate chemical structures of precursors usedto form silane-containing self-assembled monolayers (SAMs), according toone or more aspects of the present disclosure;

FIG. 9 is a cross-sectional view of a dual-gated graphene deviceaccording to one or more aspects of the present disclosure;

FIG. 10 is a cross-sectional view of a top-gated graphene deviceaccording to one or more aspects of the present disclosure;

FIG. 11 is a flow chart of a method of fabricating a carbon nanotube(CNT) according to one or more aspects of the present disclosure;

FIGS. 12, 13, 14, 15, 16, and 17 illustrate cross sectional views ofembodiments of the CNT according to one or more aspects of the presentdisclosure and corresponding to one or more steps of the method of FIG.11;

FIG. 18 is a cross-sectional view of a back-gated CNT transistoraccording to one or more aspects of the present disclosure;

FIG. 19 is a cross-sectional view of a dual-gated CNT transistoraccording to one or more aspects of the present disclosure;

FIG. 20 is a flow chart of a method of fabricating curved graphenetransistor according to one or more aspects of the present disclosure;and

FIGS. 21, 22, 23, 24, 25, 26, 27, and 28 illustrate cross sectionalviews of embodiments of the curved graphene transistor according to oneor more aspects of the present disclosure and corresponding to one ormore steps of the method of FIG. 20.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Illustrated in FIG. 1 is an exemplary back-gated graphene device 100.The graphene device 100 includes a substrate 102, an insulating layer104 disposed on the substrate 102, a graphene layer 106 disposed on theinsulating layer 104, and source/drain contacts 108 contacting thegraphene layer 106. The substrate 102 may be a semiconductor substratesuch as a silicon substrate. The substrate 102 may include variousdoping configurations depending on design requirements as is known inthe art. By way of example, the substrate 102 may include ahighly-doped, low-resistivity substrate that allows the substrate 102 tobe used as a global back-gate for the graphene device 100.

The insulating layer 104 may include a silicon dioxide (SiO₂) layergrown by thermal oxidation over the substrate 102. In some cases, athickness of the insulating layer 104 may be chosen so as to optimizethe contrast of the graphene layer 106 with respect to the underlyingsubstrate 102. By way of example, the insulating layer 104 may have athickness of about 90 nanometers (nm) or 280 nm. In some cases, theinsulating layer 104 may have a thickness in a range from about 90-100nm, or from about 280-300 nm.

The graphene layer 106 may include graphene produced by a variety ofmethods such as epitaxial growth on silicon carbide (SiC) substrates,chemical vapor deposition (CVD)-growth (e.g., involving the catalyzeddecomposition of hydrocarbons on a metal surface), and mechanicalexfoliation (e.g., from a bulk graphite source), among others. By way ofexample, the grown or exfoliated graphene layer 106 may be transferred(e.g., from a growth substrate or from the bulk graphite source) ontothe insulating layer 104 of the substrate 102, which may be referred toas a “target substrate”, upon which one or more graphene-based devicesmay be fabricated. In various examples, the graphene transfer may beaccomplished by a wet or dry transfer process. After transfer of thegraphene layer 106 onto the insulating layer 104, metal source/draincontacts 108 may be formed. The metal source/drain contacts 108 mayinclude a conductive layer such as Cr, Ti, Au, Ni, Pd, Ir, Ag, Pt, Cu,Co, Al, Fe, combinations thereof, and/or other suitable compositions.The source/drain contacts 108 may be formed using PVD, CVD, ALD,electron beam (e-beam) evaporation, and/or other suitable process. Insome examples, a device 100 active region may be defined (e.g., prior toor after formation of the source/drain contacts 108) by an appropriatephotolithography and etching process (e.g., an oxygen plasma etchingprocess). Thus, the exemplary back-gated graphene device 100 of FIG. 1includes the graphene layer 106 as the device channel, contacted bysource/drain contacts 108, and the substrate 102 is a global back-gateseparated from the graphene layer 106 by the insulating layer 104.

In various conventional methods, and as a result of the transfer of thegraphene layer 106 onto the insulating layer 104, grain boundaries,point defects, wrinkles, folds, tears, cracks, impurities, or otherdefects may be introduced into the transferred graphene layer 106 andthereby degrade the properties of any subsequently fabricated devices,such as the device 100. Thus, existing techniques have not provedentirely satisfactory in all respects.

Embodiments of the present disclosure offer advantages over the existingart, though it is understood that other embodiments may offer differentadvantages, not all advantages are necessarily discussed herein, and noparticular advantage is required for all embodiments. For example,embodiments discussed herein include methods and structures forproviding uniform, large-area graphene by way of a transfer-free,direct-growth process. In accordance with embodiments of the presentdisclosure, a self-assembled monolayer (SAM) is used as a carbon sourcefor direct graphene synthesis on a substrate. Thus, embodimentsdisclosed herein provide one or methods to avoid the introduction ofdefects into graphene, and graphene devices, which could occur as aresult of conventional graphene transfer processes, as described above.For example, in various embodiments, a carbon-containing SAM, having acontrolled number of carbon atoms therein, is formed on a substrate(e.g., an oxidized substrate), and a metal layer is formed over the SAM.The metal layer may serve as a catalytic metal (e.g., similar to themanner in which a metal layer is used for catalytic decomposition ofhydrocarbons during CVD growth of graphene), whereby thecarbon-containing SAM is converted to graphene following an appropriateannealing process. In various embodiments, the SAM is deposited using anatomic layer deposition (ALD) process, providing a highly conformal SAMhaving excellent step coverage on high-aspect ratio structures, andfacilitating SAM deposition onto any of a variety of surfaces and/orsurface topographies, such as curved surfaces and/or vertical sidewallsurfaces, among others. For example, embodiments disclosed hereinprovide for SAM deposition (and subsequent graphene conversion of theSAM by way of the catalytic metal and annealing process) not only onplanar surfaces, but also on surfaces (e.g., oxide surfaces) around thecircumference of a nanorod (e.g., an outer surface of the nanorod), aswell as on various other curved surfaces. In some embodiments, a carbonnanotube (CNT) having a controlled size (e.g., diameter, height), shape,and/or band gap, may be formed on the surface of a nanorod byappropriately tuning the geometry of the nanorod. Additionally, in someembodiments, a curved graphene transistor may be formed over a curvedoxide surface, thereby providing a band gap in a channel region of thegraphene transistor. Thus, embodiments of the present disclosure providefor the formation of high-quality, large-area graphene over any type ofsurface topography and/or surface structure, avoiding the challengesassociated with conventional graphene transfer techniques, while alsoproviding for the fabrication of CNT/graphene structures and deviceshaving desirably tuned properties.

Referring now to FIG. 2, illustrated is a flow chart of a general method200 of fabricating a graphene device according to one or more aspects ofthe present disclosure. The method 200 may be used to provide large-areagraphene using a transfer-free, direct growth process, which can therebybe used to fabricate graphene devices having improved characteristics(e.g., as a result of avoiding graphene transfer-related defects). Insome embodiments, the method 200 may be used to fabricate the device100, described above with reference to FIG. 1. Thus, one or more aspectsdiscussed above with reference to the device 100 may also apply to themethod 200. Additionally, FIGS. 9-10 are cross sectional views ofembodiments of a graphene device 300 according to one or more aspects ofthe present disclosure and corresponding to one or more steps of themethod of FIG. 2. Additional embodiments of structures and methods inaccordance with the present disclosure are discussed in more detail withreference to the methods of FIGS. 11 and 20 below.

It is understood that parts of the method 200 and/or the graphene device300 may be fabricated by a well-known complementarymetal-oxide-semiconductor (CMOS) technology process flow, and thus someprocesses are only briefly described herein. In addition, as describedabove, the device 300 may share aspects of the device 100, thus someaspects and/or processes of the device 300 are only discussed brieflyfor purposes of clarity in understanding. Further, the graphene device300 may include, and/or may be integrated with various other devices andfeatures, such as additional transistors, bipolar junction transistors,resistors, capacitors, diodes, fuses, etc., but is simplified for abetter understanding of the inventive concepts of the presentdisclosure. Further, in some embodiments, the graphene device 300includes a plurality of graphene devices (e.g., transistors), which maybe interconnected.

In various embodiments, the graphene device 300 may be an intermediatedevice fabricated during processing of an integrated circuit, or portionthereof, that may comprise static random access memory (SRAM) and/orother logic circuits, passive components such as resistors, capacitors,and inductors, and active components such as P-channel field-effecttransistors (PFETs), N-channel FETs (NFETs), metal-oxide-semiconductorfield-effect transistors (MOSFETs), complementarymetal-oxide-semiconductor (CMOS) transistors, bipolar transistors, highvoltage transistors, high frequency transistors, other memory cells,and/or combinations thereof. In some embodiments, the graphene device300 may be formed over a substrate (e.g., the substrate 102) having adielectric layer (e.g., dielectric layer 104) disposed thereon, wherethe substrate may include CMOS transistors (or other devices mentionedabove) formed within the substrate 102, and where electrodes of thegraphene device 300 (e.g., source/drain contacts 108) and electrodes ofdevices within the substrate 102 may be connected through the dielectriclayer by way of one or more contacts, vias, or other electricalinterconnects.

Referring now to the method 200, the method 200 begins at block 202where a substrate having an insulating layer is provided. Referring tothe example of FIG. 3, and in an embodiment of block 202, illustratedtherein is a device 300 including a substrate 302. The substrate 302 maybe substantially similar to the substrate 102 discussed above withreference to the device 100 of FIG. 1. For example, the substrate 302may be a semiconductor substrate such as a silicon substrate, and thesubstrate 302 may include various doping configurations depending ondesign requirements as is known in the art. In various embodiments, thesubstrate 302 may include a highly-doped (e.g., N+ or P+),low-resistivity substrate (e.g., less than 5 mOhm-cm) that allows thesubstrate 302 to be used as a global back-gate for the device 300. In afurther embodiment of block 202, an insulating layer 304 may be formedover the substrate 302. The insulating layer 304 may be substantiallysimilar to the insulating layer 104 discussed above with reference tothe device 100 of FIG. 1. For example, the insulating layer 304 mayinclude a SiO₂ layer grown by thermal oxidation over the substrate 302.However, other types of oxide layers (e.g., Al₂O₃) and/or other methodsof oxide deposition may be used (e.g., PVD, CVD, ALD) without departingfrom the scope of the present disclosure. In some embodiments, theinsulating layer 304 may have a thickness of about 90 nm or 280 nm. Insome cases, the insulating layer 304 may have a thickness in a rangefrom about 90-100 nm, or from about 280-300 nm. In various embodiments,the insulating layer 304 has a thickness that is sufficient to preventthe formation of silicides (e.g., during a subsequent annealingprocess), for example, between a subsequently deposited metal layer(e.g., metal layer 502) and the substrate 302.

The method 200 then proceeds to block 204 where a carbon-containinglayer is formed over the insulating layer. In some embodiments, thecarbon-containing layer includes a SAM or other suitablecarbon-containing layer formed using one or more suitable precursors, asdescribed below. Referring to the example of FIG. 4, and in anembodiment of block 204, a carbon-containing layer 402 is formed overthe insulating layer 304, thereby providing a carbon source forsubsequent graphene layer formation. In some embodiments, prior toforming the carbon-containing layer 402 over the insulating layer 304,the surface of the insulating layer 304 may be cleaned (e.g., to removeorganic residues). By way of example, in some embodiments, the device300 may be soaked in a piranha solution (i.e., a mixture of sulfuricacid and hydrogen peroxide) to remove organic residues from a surface ofthe insulating layer 304. In some examples, the piranha solution cleanmay be performed multiple times and for any suitable duration. By way ofexample, and in some embodiments, after cleaning the insulating layer304 using the piranha solution, the device 300 may be rinsed inultrapure water (UPW), in an ultrasonic bath, to remove residues whichmay remain from the piranha solution clean. In some embodiments, therinse/ultrasonic bath process may be performed multiple times and forany suitable duration.

In various embodiments, the carbon-containing layer 402 may be formed bya vapor phase deposition (VPD) technique such as ALD and/or molecularlayer deposition (MLD). By way of example, the ALD and MLD techniquesare both based on sequential, self-limiting surface reactions, and theymay be used to deposit organic and inorganic materials. As such,embodiments of the present disclosure employing VPD techniques provide avariety of benefits. For example, VPD deposition of thecarbon-containing layer 402 may provide a high degree of control overreactions (e.g., of precursors at a substrate surface) and layerself-assembly (e.g., without parasitic polymerization reactions).Moreover, VPD deposition provides for accurate control of a number ofcarbon atoms within the carbon-containing layer 402, directly impactingthe thickness and quality of the subsequently formed graphene layer. Invarious embodiments, VPD layer deposition may also be accomplished in arelatively short duration (e.g., in minutes), for example, as comparedto solution-based SAM formation (e.g., requiring hours). By way ofexample, VPD layer deposition is also effective at minimizing capillaryeffects, which helps to ensure a highly conformal carbon-containinglayer 402 having excellent step coverage (e.g., on high-aspect ratiostructures), and thereby facilitating deposition of thecarbon-containing layer 402 onto any of a variety of surfaces and/orsurface topographies, such as curved surfaces and/or vertical sidewallsurfaces, among others. In various embodiments, the VPD layer depositionprocesses used and described herein are clean, vacuum-based processes,they are scalable and uniform over large surface areas, they have a lowdefect density and provide reproducible layers, and they may be used toprovide heterogeneous organic and/or inorganic structures.

Returning to FIG. 4, and in various embodiments, the carbon-containinglayer 402 may include a self-assembled monolayer (SAM) formed, forexample, by a VPD method as described above. Self-assembled monolayers(SAMs), as discussed herein, may include ordered molecular assembliesthat form spontaneously by adsorption of molecules on a solid substrate.By way of example, a SAM surfactant molecule may include a head group,an alkyl chain, and an end group (functional group). The head group mayhave a high affinity to the solid substrate, and may thus chemicallyinteract with the substrate onto which it is deposited. In variousembodiments, SAM molecules may adsorb at substantially all substratesurface sites, resulting in a close-packed monolayer. In someembodiments, a SAM head groups may include organosulfurs, thiolsincluding —SH groups, or alkanethiols [X—(CH₂)n-SH] (e.g., when theunderlying surface includes a metal such as Ag, Au, and Cu, or otherappropriate metal) and silanes such as trichlorosilane (—SiCl₃),alkylsilane (—Si(CH₃)₃), or alkyltrichlorosilanes [X—(CH₂)_(n)—SiCl₃](e.g., when the underlying surface includes an oxide layer such as SiO₂,Al₂O₃, and/or other oxide/dielectric material or dielectric substrate asdescribed herein). In addition, Van der Waals interactions between SAMalkyl chains are effective to cause ordering of the SAMs. In variousembodiments, the end group is exposed at a surface, for example, uponwhich the catalytic metal layer will be formed. By way of example, theend group may include non-polar (hydrophobic) or polar (hydrophilic)functional groups such as —CH₃, —OH, —COOH, —NH₂, etc., which alsoallows the SAM to be used for the modification of surface properties.

In some embodiments, the carbon-containing layer 402 may include a SAMformed using one or more precursors selected from the group includingCH₃(CH₂)_(n)SiX₃, (C_(n)H_(2n+2))₂SiX₂, (C_(n)H_(2n+2))₃SiX,COOH(CH₂)_(n)SiX₃, NH₂(CH₂)_(n)SiX₃, CH₃(CH₂)_(n)Si(OCH₃)₃,COOH(CH₂)_(n)Si(OCH₃)₃, NH₂(CH₂)_(n)Si(OCH₃)₃, andCF₃(CF₂)_(n)(CH₂)₂SiX₃, where ‘X’ may include chlorine (Cl), bromine(Br), or iodine (I), and where ‘n’ has a value from about 1-26. In someexamples, the carbon-containing layer 402 may include a single layer ora plurality of layers (e.g., a multilayer film) and may be formed usinga VPD technique such as ALD and/or MLD. As discussed above, in variousembodiments, the carbon-containing layer 402 may include asilane-containing SAM. For example, the carbon-containing layer 402 mayinclude tridecafluoro-tetrahydrooctyl-trichlorosilane (FOTS),illustrated in FIG. 4A, which has a chemical formula C₈H₄Cl₃F₁₃Si, aboiling point of about 84 degrees Celsius, and a vapor pressure of about4.2 Torr at 70 degrees Celsius. Additionally, in some examples, thecarbon-containing layer 402 may includeheptadecafluoro-tetrahydrodecyl-trichlorosilane (FDTS), illustrated inFIG. 4B, which has a chemical formula C₁₀H₄Cl₃F₁₇Si, a boiling point ofabout 216 degrees Celsius, and a vapor pressure of about 1.7 Torr at 80degrees Celsius. In some cases, the carbon-containing layer 402 mayinclude dodecyltrichlorosilane (DTS), illustrated in FIG. 4C, which hasa chemical formula C₁₂H₂₅Cl₃Si, a boiling point of about 120 degreesCelsius, and a vapor pressure of about 0.5-1 Torr at 100 degreesCelsius.

In some embodiments, the carbon-containing layer 402 may include a SAMformed by molecular layer deposition (MLD) using one or more precursorsselected from the group including (1E)-prop-1-ene-1,2,3-tricarboxylicacid, (2E,4E)-hexa-2,4-dienedioic acid, (2S)-2-aminopentanedioic acid,(E)-butenedioic acid, (Z)-butenedioic acid,1,2-bis[(diamethylamino)dimethylsilyl]ethane, 1,4-diaminobenzene,1,4-diisocyanatobenzene, 1,4-diisocyanatobutane,1,4-diisothiocyanatobenzene, 2-aminoethanol, 2-oxepanone,4,4′-oxydianiline, 4-aminophenol, 4-nitrobenzene-1,3-diamine,7-octenyltrichlorosilane, 8-quinolinol, benzene-1,2,4,5-tetracarboxylicacid, benzene-1,2-dicarboxylic acid, benzene-1,3,5-tricarboxylic acid,benzene-1,3,5-triol, benzene-1,3-dicarboxylic acid,benzene-1,4-dicarboxylic acid, benzene-1,4-diol, benzoic acid,but-2-yne-1,4-diol, butane-1,4-diamine, butanedioic acid,decane-1,10-diamine, decanedioic acid, decanedioyl dichloride,ethane-1,2-diamine, ethane-1,2-diol, ethanedihydrazide, ethanedioicacid, ethanetetracarbonitrile, furan-2,5-dione,furo[3,4-f][2]benzofuran-1,3,5,7-tetrone, heptane-1,7-diamine,heptanedioic acid, hexa-2,4-diyne-1,6-diol, hexane-1,6-diamine,hexanedioyl dichloride, N-(2-aminoethyl)ethane-1,2-diamine,N,N-bis(2-aminoethyl)ethane-1,2-diamine, nonanedioyl dichloride,octane-1,8-diamine, octanedioic acid, octanedioyl dichloride,oxiran-2-ylmethanol, pentanedioic acid, propane-1,2,3-tricarboxylicacid, propane-1,2,3-triol, propanedioic acid, propanedioyl dichloride,terephthalaldehyde, terephthalic acid, bis(2-hydroxyethyl) ester,terephthaloyl dichloride, tris(2-aminoethyl)amine, andtris(2-hydroxyethyl)amine.

While some examples of precursors and/or materials useful for formingthe carbon-containing layer 402 (e.g., a SAM formed by way of ALD and/orMLD) have been given, the examples provided are not meant to be limitingin any way, and it will be understood that other materials may be usedto form the carbon-containing layer 402 without departing from the scopeof the present disclosure.

The method 200 then proceeds to block 206 where a metal layer is formedover the carbon-containing layer. Referring to the example of FIG. 5,and in an embodiment of block 206, a metal layer 502 is formed over thecarbon-containing layer 402 (e.g., the SAM). In various embodiments, themetal layer 502 may include Ni, Cu, Pt, Fe, Co, Au, a Cu—Ni alloy, orcombinations thereof. As referred to above, the metal layer 502 servesto facilitate the metal-catalyzed crystallization of carbon of thecarbon-containing layer 402 during a subsequent anneal process (block208), thereby converting the carbon-containing layer 402 to a graphenelayer. In various embodiments, the metal layer 502 may be formed usingPVD, CVD, ALD, electron beam (e-beam) evaporation, and/or other suitableprocess. In some embodiments, the metal layer 502 may have a thicknessof about 10 nm-500 nm.

The method 200 then proceeds to block 208 where an anneal process isformed. Referring to the example of FIGS. 5 and 6, and in an embodimentof block 208, the device 300 may be annealed in order to convert thecarbon-containing layer 402 (FIG. 5) to a graphene layer 602 (FIG. 6).In various embodiments, the conversion of the carbon-containing layer402 to the graphene layer 602 is achieved by pyrolysis. As shown in FIG.6, and as a result of the anneal process, the graphene layer 602 isformed between the metal layer 502 (e.g., the catalytic metal) and theinsulating layer 304. In some examples, the anneal process may beperformed in a hydrogen atmosphere, an argon atmosphere, a nitrogenatmosphere, or a combination thereof such as a H₂/Ar atmosphere. By wayof example, the annealing process of block 208 may be performed usingthermal radiation (e.g., thermal oven), using heat conduction (e.g., hotplate), using an optoelectronic method (e.g., laser annealing), or otherappropriate method. In various embodiments, and depending in part on thethickness of the metal layer 502, the composition of thecarbon-containing layer 402, and the annealing parameters (e.g., time,temperature, atmosphere, pressure, etc.), the graphene layer 602 mayinclude monolayer graphene, bilayer graphene, or multi-layer graphene(e.g., including more than two layers). In some embodiments, the annealprocess of block 208 may be performed at a temperature from about600-1200 degrees Celsius. In some embodiments, the anneal process ofblock 208 may be performed for a duration of between about 1-60 minutes.

The method 200 then proceeds to block 210 where the metal layer isremoved and a thermal treatment in a reducing atmosphere is performed.Referring to the example of FIGS. 6 and 7, and in an embodiment of block210, the metal layer 502 may be removed. In various embodiments, anddepending on the material used for the metal layer 502 (e.g., Ni, Cu,Pt, Fe, Co, Au, a Cu—Ni alloy, or combinations thereof), the metal layer502 may be removed using an etching solution including, for example,ferric chloride (FeCl₃), hydrochloric acid (HCl), nitric acid (HNO₃),ammonium persulfate (NH₄)₂S₂O₈, or other metal etching solutions asknown in the art. Thus, as shown in FIG. 7, the graphene layer 602 hasbeen directly formed on the insulating layer 304 using a transfer-freeprocess. After removal of the metal layer 502, and in a furtherembodiment of the block 210, the now exposed graphene layer 602 may bethermally treated in a reducing atmosphere. For example, in someembodiments, the device 300 may be annealed at a temperature of about800-1200 degrees Celsius in a H₂/Ar atmosphere, in a H₂/N₂ atmosphere,in a N₂H₂ atmosphere, or in another appropriate reducing atmosphere.

The method 200 then proceeds to block 212 where electrodes are formed.Referring to the example of FIG. 8, after performing the thermaltreatment in the reducing atmosphere and in an embodiment of block 212,source/drain electrodes 802 may be formed over the graphene layer 602.In some embodiments, the source/drain electrodes 802 may include aconductive layer such as Cr, Ti, Au, Ni, Pd, Ir, Ag, Pt, Cu, Co, Al, Fe,combinations thereof, and/or other suitable compositions. In variousembodiments, the source/drain electrodes 802 may be formed using PVD,CVD, ALD, electron beam (e-beam) evaporation, and/or other suitableprocess. In some examples, the source/drain electrodes 802 may be formedusing a metal lift-off process. In some examples, a device 300 activeregion may be defined (e.g., prior to or after formation of thesource/drain electrodes 802) by an appropriate photolithography andetching process (e.g., an oxygen plasma etching process). Thus, thedevice 300 of FIG. 8 includes a back-gated graphene device, where thedirectly formed, transfer-free graphene layer 602 is contacted bysource/drain electrodes 802, and the substrate 302 serves as a globalback-gate separated from the graphene layer 602 by the insulating layer304. In some cases, a metal layer (e.g., Al) may be evaporated onto asurface 804 of the substrate 302 in order to improve contact to thesubstrate 302.

The device 300 may undergo further processing to form various featuresand regions known in the art. For example, subsequent processing mayform various contacts/vias/lines and multilayers interconnect features(e.g., metal layers and interlayer dielectrics) on the substrate 302,configured to connect the various features to form a functional circuitthat may include one or more graphene devices. In furtherance of theexample, a multilayer interconnection may include verticalinterconnects, such as vias or contacts, and horizontal interconnects,such as metal lines. The various interconnection features may employvarious conductive materials including copper, tungsten, and/orsilicide. In one example, a damascene and/or dual damascene process isused to form a copper related multilayer interconnection structure. Insome embodiments, the graphene device 300 may be formed over a substratehaving a dielectric layer disposed thereon, where the substrate mayinclude CMOS transistors (or other devices mentioned above) formedwithin the substrate, and where electrodes of the graphene device 300(e.g., source/drain electrodes 802) and electrodes of devices within thesubstrate may be connected through the dielectric layer by way of one ormore contacts, vias, or other electrical interconnects. Moreover,additional process steps may be implemented before, during, and afterthe method 200, and some process steps described above may be replacedor eliminated in accordance with various embodiments of the method 200.

With reference now to FIG. 9, illustrated therein is a cross-sectionalview of a dual-gated graphene device 900 according to one or moreaspects of the present disclosure. In various embodiments, the device900 may be processed in a manner substantially similar to the device 300described above with respect to the method 200. By way of illustration,after formation of the back-gated device, as shown in FIG. 8, additionalprocessing may be performed to fabricate the dual-gated device of FIG.9. For example, in some embodiments, after formation of the source/drainelectrodes 802, a top-gate dielectric layer 902 may be formed over thegraphene layer 602. Due to the inert nature of graphene, in someexamples, a nucleation and/or functionalization layer (ornucleation/functionalization treatment) may be formed (or performed)prior to formation of the dielectric layer 902 in order to enable thedeposition of the dielectric layer 902 onto the graphene layer 602.Merely for purposes of illustration, in some embodiments, an Alnucleation layer may be formed prior to deposition of an Al₂O₃ layer.For further illustration, in some examples, an ozone (O₃) pre-treatmentmay be performed prior to deposition of the dielectric layer 902. Whilesome examples of forming a nucleation layer on graphene, or ofperforming a functionalization treatment, have been provided, theseexamples are not meant to be limiting in any way, and those of skill inthe art will recognize other nucleation layers and/or functionalizationtreatments that may be performed without departing from the scope of thepresent disclosure.

In various embodiments, the dielectric layer 902 may include a high-Kdielectric layer. High-K dielectrics, as used and described herein,include dielectric materials having a high dielectric constant, forexample, greater than that of thermal silicon oxide (˜3.9). In variousembodiments, the high-K dielectric layer of the dielectric layer 902 mayinclude a dielectric layer such as HfO₂ TiO₂, HfZrO, Ta₂O₃, HfSiO₄,ZrO₂, ZrSiO₂, LaO, AlO, ZrO, TiO, Ta₂O₅, Y₂O₃, SrTiO₃ (STO), BaTiO₃(BTO), BaZrO, HfZrO, HfLaO, HfSiO, LaSiO, AlSiO, HfTaO, HfTiO,(Ba,Sr)TiO₃ (BST), Al₂O₃, Si₃N₄, oxynitrides (SiON), combinationsthereof, or other suitable material. In some embodiments, the high-Kdielectric layer of the dielectric layer 902 may be formed by ALD,physical vapor deposition (PVD), CVD, chemical oxidation, thermaloxidation, and/or other suitable methods.

Still referring to FIG. 9, after formation of the dielectric layer 902,a top-gate electrode 904 may be formed. By way of example, in someembodiments, the top-gate electrode 904 may include a conductive layersuch as W, TiN, TaN, WN, Re, Ir, Ru, Mo, Al, Cu, Co, Ni, Cr, Ti, Au, Pd,Ag, Pt, Fe, combinations thereof, and/or other suitable compositions. Insome embodiments, the top-gate electrode 904 may alternately include apolysilicon layer. The top-gate electrode 904 may be formed using PVD,CVD, ALD, electron beam (e-beam) evaporation, and/or other suitableprocess. In some examples, the top-gate electrode 904 may be formedusing a metal lift-off process. Thus, the device 900 of FIG. 9 providesa dual-gate structure, including the directly formed, transfer-freegraphene layer 602 (device channel), and including the substrate 302 asthe global back-gate and the top-gate electrode 904 as a top-gate.

Referring to FIG. 10, illustrated therein is a cross-sectional view of atop-gated graphene device 1000 according to one or more aspects of thepresent disclosure. In various embodiments, aspects of the device 1000may be formed in a manner similar to the device 300 described above withrespect to the method 200, and/or as discussed above with reference tothe device 900 of FIG. 9. By way of illustration, and in an embodimentof block 204 of the method 200, the carbon-containing layer 402 isformed over an insulating layer. However, in the example of FIG. 10, theinsulating layer (on which the graphene layer is directly formed)includes an insulating substrate 1002. For example, in variousembodiments, the insulating substrate 1002 may include quartz, glass,ceramic, sapphire, silicon carbide (SiC), as well as other insulating orsemi-insulating substrates as known in the art. In at least someembodiments, an insulating substrate may be beneficial forradio-frequency (RF) graphene devices. After direct growth of thegraphene layer 602 to the insulating substrate 1002, using atransfer-free process as described above, the device 1000 may beprocessed substantially the same as described above. For example, theannealing process may be performed (block 208), the source/drainelectrodes 802 may be formed, and the dielectric layer 902/top-gate 904may be formed. Thus, the device 1000 of FIG. 10 provides a top-gatestructure including the directly formed, transfer-free graphene layer602 (device channel), and the top-gate electrode 904 as a top-gate. Itis noted that the device 1000 does not include a global back-gate due tothe insulating substrate 1002.

Referring now to FIG. 11, illustrated is a flow chart of a method 1100of fabricating a carbon nanotube (CNT) having a controlled size (e.g.,diameter, height, etc.), and related device, according to one or moreaspects of the present disclosure. The method 1100 shares variousfeatures with the method 200 discussed above, while providing additionalembodiments in accordance with the present disclosure. As describedbelow, in some embodiments, the method 1100 may be used to providegraphene around a circumference of a nanorod (e.g., an outer surface ofthe nanorod) having an insulating (e.g., oxide) surface by way of thetransfer-free, direct growth process, thereby forming a CNT thatconforms to the geometry of the insulating nanorod surface. In variousembodiments, one or more aspects discussed above with reference to thedevice 300 may also apply to the method 1100. Additionally, FIGS. 18-19are cross sectional views of embodiments of a CNT transistor accordingto one or more aspects of the present disclosure and corresponding toone or more steps of the method of FIG. 11.

It is understood that parts of the method 1100 and/or the CNT device1300 may be fabricated by a well-known complementarymetal-oxide-semiconductor (CMOS) technology process flow, and thus someprocesses are only briefly described herein. In addition, as describedabove, the CNT device 1300 may share aspects of the device 300, thussome aspects and/or processes of the device 1300 are only discussedbriefly for purposes of clarity in understanding. Further, the CNTdevice 1300 may include, and/or may be integrated with various otherdevices and features, such as additional transistors, bipolar junctiontransistors, resistors, capacitors, diodes, fuses, etc., but issimplified for a better understanding of the inventive concepts of thepresent disclosure. Further, in some embodiments, the CNT device 1300includes a plurality of graphene devices (e.g., transistors), which maybe interconnected.

The method 1100 begins at block 1102 where a nanorod with an insulatingsurface (e.g., an oxide surface) is formed. Referring to the example ofFIG. 12, and in an embodiment of block 1102, illustrated therein is asubstrate 1202 including a plurality of nanorods 1204 (e.g., a nanorodarray) extending therefrom, wherein the nanorods 1204 have insulatingsurfaces. While the embodiments are discussed herein as nanorods, it isunderstood that other one-dimensional nanostructures such as nanowiresor nanopillars may equally be used without departing from the scope ofthe present disclosure. In some embodiments, the substrate 1202 may besubstantially similar to the substrate 302 or the substrate 102discussed above. For example, the substrate 1202 may be a semiconductorsubstrate such as a silicon substrate, and the substrate 1202 mayinclude various doping configurations depending on design requirementsas is known in the art. In various embodiments, the nanorods 1204 may beformed by any suitable technique including top-down or bottom-upapproaches, and including lithography and etching, anodic aluminum oxide(AAO) templates, colloidal templates, solution-based growth, vapor-basedgrowth, or other suitable technique as known in the art. Additionally,in various examples, the nanorods 1204 may initially be formed asmetallic nanorods, semiconducting nanorods, or insulating nanorods, andan insulating layer may be subsequently formed over the nanorod 1204surface. With reference to the example of FIG. 13, illustrated thereinis the CNT device 1300 including an individual nanorod 1204 (e.g., ofthe nanorod array shown in FIG. 12), where the nanorod 1204 has aninsulating surface. For the sake of clarity, the discussion that followswill be provided with reference to the individual nanorod 1204, asillustrated in FIG. 13. Generally, after nanorod formation and in someembodiments, an insulating layer (e.g., an oxide layer) may be formedover the surface of the nanorod such that irrespective of the type ofnanorod initially formed (e.g., metallic, semiconducting, insulating),the nanorod 1204 will have an insulating surface 1302 formed thereupon.In some cases, for example if the initially formed nanorod 1204 includesan insulating nanorod, then an additional insulating layer formed overthe surface of the nanorod 1204 may be optional. By way of example, theinsulating layer used to form the insulating surface 1302 may includeSiO₂, Al₂O₃, or other appropriate insulating layer, and the insulatinglayer may be deposited over the nanorod surface by thermal oxidation,CVD, ALD, PVD, or other suitable technique. In accordance withembodiments of the present disclosure, dimensions of the nanorod 1204(e.g., diameter, height, etc.), as well as the thickness of anyinsulating layer deposited on the nanorod 1204, may be selected so as todefine a geometry of a nanorod with an insulating surface upon which aCNT will be formed. With reference to FIG. 13, the geometry of thenanorod 1204 with the insulating surface may be defined at least in partby a diameter ‘D’ and a height ‘H’. Thus, in accordance with variousembodiments, a CNT having a controlled diameter ‘D’ may be fabricated,based on the geometry of the nanorod 1204 with the insulating surface.Moreover, it is known that CNT band gap (e.g., at least for single-wallCNTs) varies as a function of CNT diameter. Thus, in accordance withsome embodiments, a CNT having a controlled band gap may be fabricated,thereby ensuring formation of an appropriate semiconducting CNT forsubsequent transistor fabrication.

The method 1100 then proceeds to block 1104 where a carbon-containinglayer is formed over the insulating layer. Referring to the example ofFIG. 14, and in an embodiment of block 1104, a carbon-containing layer1402 is formed over the insulating surface 1302 of the nanorod 1204,thereby providing a carbon source for subsequent graphene layerformation around the circumference of the nanorod 1204 (e.g., an outersurface of the nanorod). In some embodiments, prior to forming thecarbon-containing layer 1402 over the insulating surface 1302 of thenanorod 1204, the insulating surface 1302 of the nanorod 1204 may becleaned (e.g., to remove organic residues), for example, using a piranhasolution and UPW rinse as described above.

In various embodiments, the composition and method of formation of thecarbon-containing layer 1402 is substantially the same as thecarbon-containing layer 402 discussed above with reference to the method200. Thus, in some embodiments, the carbon-containing layer 1402 maylikewise include a SAM or other suitable carbon-containing layer formedusing one or more suitable precursors, as described above. In at leastsome embodiments, the carbon-containing layer 1402 includes asilane-based SAM, as described above. Additionally, thecarbon-containing layer 1402 may also be formed by a VPD technique suchas ALD and/or MLD, thereby effectively forming the carbon-containinglayer 1402 on the surface 1302 of the nanorod 1204 (e.g., an outersurface of the nanorod traversing the circumference of the nanorod1204). In various examples, any of the precursors and/or materialsdiscussed above as useful for forming the carbon-containing layer 402(e.g., by way of ALD and/or MLD) for the device 300 may likewise be usedto form the carbon-containing layer 1402 for the device 1300.

The method 1100 then proceeds to block 1106 where a metal layer isformed over the carbon-containing layer. Referring to the example ofFIG. 15, and in an embodiment of block 1106, a metal layer 1502 isformed over the carbon-containing layer 1402 (e.g., the SAM). In variousembodiments, the metal layer 1502 may include Ni, Cu, Pt, Fe, Co, Au, aCu—Ni alloy, or combinations thereof. As discussed above, the metallayer 1502 serves to facilitate the metal-catalyzed crystallization ofcarbon of the carbon-containing layer 1402 during a subsequent annealprocess (block 1108), thereby converting the carbon-containing layer1402 to a graphene layer wrapped around the nanorod 1204, therebyeffectively forming a CNT around the circumference of the nanorod 1204.In various embodiments, the metal layer 1502 may be formed using PVD,CVD, ALD, electron beam (e-beam) evaporation, and/or other suitableprocess.

The method 1100 then proceeds to block 1108 where an anneal process isformed. Referring to the example of FIGS. 15 and 16, and in anembodiment of block 1108, the CNT device 1300 may be annealed in orderto convert the carbon-containing layer 1402 (FIG. 15) to a CNT 1602(FIG. 16). In various embodiments, the conversion of thecarbon-containing layer 1402 to the CNT 1602 is achieved by pyrolysis.As shown in FIG. 16, and as a result of the anneal process, the CNT 1602is formed between the metal layer 1502 (e.g., the catalytic metal) andthe insulating surface 1302 of the nanorod 1204. In some examples, theanneal process may be performed in a hydrogen atmosphere, an argonatmosphere, a nitrogen atmosphere, or a combination thereof such as aH₂/Ar atmosphere. By way of example, the annealing process of block 1108may be performed using thermal radiation (e.g., thermal oven), usingheat conduction (e.g., hot plate), using an optoelectronic method (e.g.,laser annealing), or other appropriate method. In various embodiments,and depending in part on the thickness of the metal layer 1502, thecomposition of the carbon-containing layer 1402, and the annealingparameters (e.g., time, temperature, atmosphere, pressure, etc.), theCNT 1602 may include monolayer CNT (e.g., single-wall CNT), bilayer CNT(e.g., double-wall CNT), or multi-layer CNT (e.g., multi-wall CNT).

The method 1100 then proceeds to block 1110 where the metal layer isremoved and a thermal treatment in a reducing atmosphere is performed.Referring to the example of FIGS. 16 and 17, and in an embodiment ofblock 1110, the metal layer 1502 may be removed. In various embodiments,and depending on the material used for the metal layer 1502 (e.g., Ni,Cu, Pt, Fe, Co, Au, a Cu—Ni alloy, or combinations thereof), the metallayer 1502 may be removed using an etching solution including, forexample, ferric chloride (FeCl₃), hydrochloric acid (HCl), nitric acid(HNO₃), ammonium persulfate (NH₄)₂S₂O₈, or other metal etching solutionsas known in the art. Thus, as shown in FIG. 17, the CNT 1602 has beendirectly formed on the insulating surface 1302 of the nanorod 1204 usinga transfer-free process. After removal of the metal layer 1502, and in afurther embodiment of the block 1110, the now exposed CNT 1602 may bethermally treated in a reducing atmosphere. For example, in someembodiments, the CNT device 1300 may be annealed at a temperature ofabout 800-1200 degrees Celsius in a H₂/Ar atmosphere, in a H₂/N₂atmosphere, in a N₂H₂ atmosphere, or in another appropriate reducingatmosphere.

The device 1300 may undergo further processing to form various featuresand regions known in the art. For example, subsequent processing may beperformed to fabricate a CNT transistor using the device 1300. Forexample, FIGS. 18-19 are cross sectional views of embodiments of a CNTtransistor 1800 and a CNT transistor 1900, according to one or moreaspects of the present disclosure. The CNT transistor 1800 may besimilar in some aspects to the device 300 of FIG. 8, where the graphenelayer 602 is replaced with the device 1300 (CNT channel), which in someexamples, may be transferred onto an insulating substrate or substratehaving an insulating layer formed thereupon. Thus, by way of example,the CNT transistor 1800 of FIG. 18 may include a back-gated CNTtransistor, where the device 1300 is contacted by source/drainelectrodes 1802, and a substrate 1802 serves as a global back-gateseparated from the device 1300 by an insulating layer 1804. In somecases, a metal layer (e.g., Al) may be evaporated onto a surface 1806 ofthe substrate 1802 in order to improve contact to the substrate 1802.Similarly, the CNT transistor 1900 may be similar in some aspects to thedevice 900 of FIG. 9, where the CNT transistor 1900 provides a dual-gatestructure, including the device 1300 contacted by source/drainelectrodes 1802, the substrate 1802 as a global back-gate separated fromthe device 1300 by the insulating layer 1804, a top-gate dielectriclayer 1902 formed over the device 1300, and top-gate electrode 1904formed over the top-gate dielectric layer 1902. In various embodiments,the top-gate dielectric layer 1902 and top-gate electrode 1904 mayinclude one or more materials, and be formed by one or more methods, asdescribed above. In some embodiments, a CNT device 1300 may also be usedto fabricate a top-gated CNT transistor, where the substrate includes aninsulating substrate (e.g., for RF applications), such as describedabove with reference to FIG. 10.

In various aspects, the device 1300 and/or the CNT transistors 1800,1900 may undergo further processing to form various contacts/vias/linesand multilayers interconnect features (e.g., metal layers and interlayerdielectrics), for example, configured to connect the various features toform a functional circuit that may include one or more CNT devices. Infurtherance of the example, a multilayer interconnection may includevertical interconnects, such as vias or contacts, and horizontalinterconnects, such as metal lines. The various interconnection featuresmay employ various conductive materials including copper, tungsten,and/or silicide. In one example, a damascene and/or dual damasceneprocess is used to form a copper related multilayer interconnectionstructure. In some embodiments, the CNT transistors 1800, 1900 may beformed over a substrate having a dielectric layer disposed thereon,where the substrate may include CMOS transistors (or other devicesmentioned above) formed within the substrate, and where electrodes ofthe CNT transistors 1800, 1900 (e.g., source/drain electrodes 1802) andelectrodes of devices within the substrate may be connected through thedielectric layer by way of one or more contacts, vias, or otherelectrical interconnects. Moreover, additional process steps may beimplemented before, during, and after the method 1100, and some processsteps described above may be replaced or eliminated in accordance withvarious embodiments of the method 1100.

Referring now to FIG. 20, illustrated is a flow chart of a method 2000of fabricating a curved graphene transistor 2100, according to one ormore aspects of the present disclosure. The method 2000 shares variousfeatures with the method 200 discussed above, while providing additionalembodiments in accordance with the present disclosure. As describedbelow, in some embodiments, the method 2000 may be used to form grapheneover a curved oxide surface, by way of the transfer-free, direct growthprocess disclosed herein, thereby providing a band gap in a channelregion of the graphene transistor. In various embodiments, one or moreaspects discussed above with reference to the device 300 may also applyto the method 2000.

It is understood that parts of the method 2000 and/or the curvedgraphene transistor 2100 may be fabricated by a well-known complementarymetal-oxide-semiconductor (CMOS) technology process flow, and thus someprocesses are only briefly described herein. In addition, as describedabove, the curved graphene transistor 2100 may share aspects of thedevice 300, thus some aspects and/or processes of the curved graphenetransistor 2100 are only discussed briefly for purposes of clarity inunderstanding. Further, the curved graphene transistor 2100 may include,and/or may be integrated with various other devices and features, suchas additional transistors, bipolar junction transistors, resistors,capacitors, diodes, fuses, etc., but is simplified for a betterunderstanding of the inventive concepts of the present disclosure.Further, in some embodiments, the curved graphene transistor 2100includes a plurality of curved graphene devices (e.g., transistors),which may be interconnected.

The method 2000 begins at block 2002 where a curved substrate having aninsulating layer is provided. Referring to the example of FIG. 21, andin an embodiment of block 2002, illustrated therein is a device 2100including a substrate 2102 having a curved region 2105 (e.g., a concaveregion 2105). In various embodiments, the concave curved region 2105 maybe formed, for example, by a lithography process, a wet etch process, adry etch process, a combination thereof, and/or other suitable process.The substrate 2102 may be substantially similar to the substrate 302discussed above with reference to the device 300 of the method 200 ofFIG. 2. Thus, the substrate 2102 may similarly include a highly-doped(e.g., N+ or P+), low-resistivity substrate (e.g., less than 5 mOhm-cm)that allows the substrate 2102 to be used as a global back-gate for thedevice 2100. In a further embodiment of block 2002, and again similar tothe device 300, an insulating layer 2104 may be formed over thesubstrate 2102. The insulating layer 2104 may be substantially similarto the insulating layer 304 discussed above with reference to the device300. Additionally, as shown in FIG. 21, the insulating layer 2104 mayconform to the substrate 2102, such that the insulating layer 2104 alsofollows a surface contour of the substrate curved region 2105. Asdescribed above, the thickness of the insulating layer 2104 is thickenough to prevent the formation of silicides (e.g., during a subsequentannealing process). With reference to the example of FIG. 22, and in anadditional embodiment of block 2002, a device 2200 including a substrate2102 having a curved region 2205 may be provided, where the curvedregion 2205 includes a convex region 2205 (e.g., in contrast to theconcave region 2105 of FIG. 21). In various embodiments, the convexcurved region 2205 may be formed, for example, by a lithography process,a deposition process, a wet etch process, a dry etch process, acombination thereof, and/or other suitable process. For purposes of thediscussion that follows, the method 2000 will be primarily discussedwith reference to the device 2100 including the concave curved region2105.

The method 2000 then proceeds to block 2004 where a carbon-containinglayer is formed over the curved insulating layer 2104. Referring to theexample of FIG. 23, and in an embodiment of block 2004, acarbon-containing layer 2302 is formed over the insulating layer 2104,thereby providing a carbon source for subsequent graphene layerformation. In some embodiments, prior to forming the carbon-containinglayer 2302 over the insulating layer 2104, the surface of the insulatinglayer 2104 may be cleaned (e.g., to remove organic residues), forexample, using a piranha solution and UPW rinse as described above.

In various embodiments, the composition and method of formation of thecarbon-containing layer 2302 is substantially the same as thecarbon-containing layer 402 discussed above with reference to the device300 and the method 200. Thus, in some embodiments, the carbon-containinglayer 2302 may likewise include a SAM or other suitablecarbon-containing layer formed using one or more suitable precursors, asdescribed above. In at least some embodiments, the carbon-containinglayer 2302 includes a silane-based SAM, as described above.Additionally, the carbon-containing layer 2302 may also be formed by aVPD technique such as ALD and/or MLD, thereby effectively andconformally forming the carbon-containing layer 2302 on the insulatinglayer 2104 and along the concave region 2105. In various examples, anyof the precursors and/or materials discussed above as useful for formingthe carbon-containing layer 402 (e.g., by way of ALD and/or MLD) for thedevice 300 may likewise be used to form the carbon-containing layer 2302for the device 2100 (or the device 2200).

The method 2000 then proceeds to block 2006 where a metal layer isformed over the carbon-containing layer. Referring to the example ofFIG. 24, and in an embodiment of block 2006, a metal layer 2402 isformed over the carbon-containing layer 2302 (e.g., the SAM). Asdescribed above, and in various embodiments, the metal layer 2402 mayinclude Ni, Cu, Pt, Fe, Co, Au, a Cu—Ni alloy, or combinations thereof.In various embodiments, the metal layer 2402 may be formed using PVD,CVD, ALD, electron beam (e-beam) evaporation, and/or other suitableprocess.

The method 2000 then proceeds to block 2008 where an anneal process isformed. Referring to the example of FIGS. 24 and 25, and in anembodiment of block 2008, the device 2100 may be annealed in order toconvert the carbon-containing layer 2302 (FIG. 24) to a graphene layer2502 (FIG. 25). In various embodiments, the conversion of thecarbon-containing layer 2302 to the graphene layer 2502 is achieved bypyrolysis. As shown in FIG. 25, and as a result of the anneal process,the graphene layer 2502 is formed between the metal layer 2402 (e.g.,the catalytic metal) and the insulating layer 2104. In various examples,the anneal process may be performed as described above with reference toblock 208 of the method 200. In various embodiments, and depending inpart on the thickness of the metal layer 2402, the composition of thecarbon-containing layer 2302, and the annealing parameters (e.g., time,temperature, atmosphere, pressure, etc.), the graphene layer 2502 mayinclude monolayer graphene, bilayer graphene, or multi-layer graphene(e.g., including more than two layers).

The method 2000 then proceeds to block 2010 where the metal layer isremoved and a thermal treatment in a reducing atmosphere is performed.Referring to the example of FIGS. 25 and 26, and in an embodiment ofblock 2010, the metal layer 2402 may be removed. In various embodiments,and depending on the material used for the metal layer 2402 (e.g., Ni,Cu, Pt, Fe, Co, Au, a Cu—Ni alloy, or combinations thereof), the metallayer 2402 may be removed using an etching solution including, forexample, ferric chloride (FeCl₃), hydrochloric acid (HCl), nitric acid(HNO₃), ammonium persulfate (NH₄)₂S₂O₈, or other metal etching solutionsas known in the art. Thus, as shown in FIG. 26, the curved graphenelayer 2502 has been directly formed on the insulating layer 2104 using atransfer-free process. Moreover, the graphene layer 2502 follows thesurface contour of the underlying insulating layer/substrate. Afterremoval of the metal layer 2402, and in a further embodiment of theblock 2010, the now exposed curved graphene layer 2502 may be thermallytreated in a reducing atmosphere. For example, in some embodiments, thedevice 2100 may be annealed at a temperature of about 800-1200 degreesCelsius in a H₂/Ar atmosphere, in a H₂/N₂ atmosphere, in a N₂H₂atmosphere, or in another appropriate reducing atmosphere.

Still referring to FIG. 26, illustrated therein is the curved (e.g.,concave) region 2105 and regions 2605 adjacent to and on either side ofthe curved region 2105. In some embodiments, the regions 2605 aresubstantially planar and/or not intentionally processed to includecurved regions, for example as described above with respect to formationof the curved region 2105. As such, the graphene layer 2502 (whichconforms to the curvature of the underlying insulating layer 2104) iscurved in the region 2105 and is substantially planar in the regions2605. As a result of the curvature of the graphene layer 2502 within theregion 2105, a band gap may be induced to open in the graphene layer2502 within the curved region 2105, whereby the graphene layer 2502 mayexhibit semiconducting behavior within the curved region 2105. In someembodiments, band gap may be induced to open in the graphene layer 2502within the curved region 2105 when a non-zero electric field is appliedto the graphene layer 2502. Additionally, in some embodiments, thegraphene layer 2502 within the substantially planar regions 2605 maymaintain a band gap substantially equal to zero, thereby exhibitingmetallic behavior in the regions 2605. As used herein, the term“substantially planar” may be used to include planar graphene layers, aswell as graphene layers having non-zero curvature, but where suchnon-zero curvature is insufficient to induce opening of a band gapwithin the graphene layer. In contrast, the curvature of the graphenelayer (e.g., within the region 2105) is sufficient to induce opening ofthe band gap in the graphene layer, as described above, either by way ofthe curvature of the curved region 2105 alone, or in conjunction with anapplied electric field. Thus, the device 2100 (or the device 2200) canbe used to provide a graphene having a seamless transition betweensemiconducting graphene in the region 2105 (which will form a graphenedevice channel) and metallic graphene in regions 2605 (which will formgraphene source/drain regions).

The method 2000 then proceeds to block 2012 where electrodes are formed.Referring to the example of FIG. 27, after performing the thermaltreatment in the reducing atmosphere and in an embodiment of block 2012,source/drain electrodes 2702 and a gate electrode 2704 may be formed.The curved graphene transistor 2100 may be similar in some aspects tothe device 300 as discussed above with reference to the method 200. Forexample, the graphene layer 2502 may be contacted in regions 2605(metallic regions) by the source/drain electrodes 2702, a top-gatedielectric layer 2703 may be formed over the graphene layer 2502 inregion 2105 (semiconducting region), and the top-gate electrode 27004may be formed over the top-gate dielectric layer 2703. In variousembodiments, the source/drain electrodes 2702, the top-gate dielectriclayer 2703, and the top-gate electrode 2702 may include one or morematerials, and be formed by one or more methods, as described above withreference to the device 300. In some embodiments, the substrate 2102 mayalso serve as a global back-gate separated from the graphene layer 2502by the insulating layer 2104. In some embodiments, the device 2100 mayinclude a top-gated curved graphene transistor, where the substrateincludes an insulating substrate (e.g., for RF applications), such asdescribed above with reference to FIG. 10. With reference to the exampleof FIG. 28, and in an additional embodiment of block 2012, electrodesmay be formed on the device 2200 including the curved convex region2205.

The device 2100 (or the device 2200) may undergo further processing toform various features and regions known in the art. For example,subsequent processing may form various contacts/vias/lines andmultilayers interconnect features (e.g., metal layers and interlayerdielectrics) on the substrate 2102, configured to connect the variousfeatures to form a functional circuit that may include one or moregraphene devices. In furtherance of the example, a multilayerinterconnection may include vertical interconnects, such as vias orcontacts, and horizontal interconnects, such as metal lines. The variousinterconnection features may employ various conductive materialsincluding copper, tungsten, and/or silicide. In one example, a damasceneand/or dual damascene process is used to form a copper relatedmultilayer interconnection structure. In some embodiments, the curvedgraphene devices 2100, 2200 may be formed over a substrate having adielectric layer disposed thereon, where the substrate may include CMOStransistors (or other devices mentioned above) formed within thesubstrate, and where electrodes of the graphene devices 2100, 2200(e.g., source/drain electrodes 2702) and electrodes of devices withinthe substrate may be connected through the dielectric layer by way ofone or more contacts, vias, or other electrical interconnects. Moreover,additional process steps may be implemented before, during, and afterthe method 2000, and some process steps described above may be replacedor eliminated in accordance with various embodiments of the method 2000.

The various embodiments described herein offer several advantages overthe existing art. It will be understood that not all advantages havebeen necessarily discussed herein, no particular advantage is requiredfor all embodiments, and other embodiments may offer differentadvantages. As one example, embodiments discussed herein include methodsand structures for providing uniform, large-area graphene by way of atransfer-free, direct-growth process. In accordance with at least someembodiments of the present disclosure, a SAM is used as a carbon sourcefor direct graphene synthesis on a substrate. Thus, embodimentsdisclosed herein provide one or methods to avoid the introduction ofdefects into graphene, and graphene devices, which could occur as aresult of conventional graphene transfer processes, as described above.For example, in various embodiments, a carbon-containing SAM is formedon a substrate having an oxide layer (which may be curved), or on a CNT(or nanorod) with an oxide layer covering an outer CNT surface (or anouter nanorod surface), and a metal layer is formed over the SAM. Themetal layer may serve as a catalytic metal, whereby thecarbon-containing SAM is converted to graphene following an appropriateannealing process. In various embodiments, the SAM is deposited using aVPD process (e.g., an ALD process and/or an MLD process), providing ahighly conformal SAM having excellent step coverage on high-aspect ratiostructures, and facilitating SAM deposition onto any of a variety ofsurfaces and/or surface topographies. For example, embodiments disclosedherein provide for SAM deposition (and subsequent graphene conversion ofthe SAM by way of the catalytic metal and annealing process) not only onplanar surfaces, but also on surfaces (e.g., oxide surfaces) around thecircumference of a nanorod (e.g., an outer surface of the nanorod, forsubsequent CNT formation), as well as on various other curved surfaces.In some embodiments, a CNT having a controlled size (e.g., diameter,height), shape, and/or band gap, may be formed on the surface of ananorod by appropriately tuning the geometry of the nanorod.Additionally, in some embodiments, a curved graphene transistor may beformed over a curved oxide surface, thereby providing a band gap in achannel region of the graphene transistor. Thus, embodiments of thepresent disclosure provide for the formation of high-quality, large-areagraphene over any type of surface topography and/or surface structure,avoiding the challenges associated with conventional graphene transfertechniques, while also providing for the fabrication of CNT/graphenestructures and devices having desirably tuned properties.

Thus, one of the embodiments of the present disclosure described amethod for fabricating a device (e.g., a graphene device), where themethod includes providing a substrate including an insulating layerdisposed thereon. In various embodiments, a carbon-containing layer isformed over the insulating layer by a vapor phase deposition process(e.g., ALD and/or MLD). Thereafter, a metal layer is deposited over thecarbon-containing layer. By way of example, after depositing the metallayer, an annealing process is performed, where the annealing processserves to convert the carbon-containing layer into a graphene layer.

In another of the embodiments, discussed is a method where a substrateincluding a nanorod extending therefrom is provided. In variousexamples, the nanorod includes an insulating outer surface thattraverses a circumference of the nanorod. In some embodiments, acarbon-containing layer is formed over the insulating outer surface by avapor phase deposition process, and a metal layer is deposited over thecarbon-containing layer. In various embodiments, after depositing themetal layer, an annealing process is performed, where the annealingprocess serves to convert the carbon-containing layer into a carbonnanotube (CNT).

In yet another of the embodiments, discussed is a device including asubstrate having a first surface contour defined by a first region and asecond region adjacent to and on either side of the first region. Thefirst region includes a curved region and the second region includes asubstantially planar region. In some embodiments, the device furtherincludes an insulating layer formed over the first and second regions ofthe substrate, where the insulating layer includes a second surfacecontour that conforms to the first surface contour of the substrate. Byway of example, the device also includes a graphene layer formed overthe insulating layer, where the graphene layer includes a third surfacecontour that conforms to the second surface contour of the insulatinglayer. Further, the graphene layer over the first region includes acurved graphene layer, and the graphene layer over the second regionincludes a substantially planar graphene layer. In some embodiments, thedevice may also include source and drain electrodes in contact with thegraphene layer in the second region.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A device, comprising: a substrate having a firstsurface that includes a curved region; a conformal graphene layerdisposed over the substrate, wherein the conformal graphene layerincludes a second surface that follows a first surface contour of thecurved region to provide a curved graphene layer within the curvedregion; and a source/drain electrode in contact with the conformalgraphene layer outside the curved region.
 2. The device of claim 1,wherein the substrate includes an insulating substrate.
 3. The device ofclaim 2, wherein the insulating substrate includes one of quartz, glass,ceramic, sapphire, and silicon carbide (SiC).
 4. The device of claim 1,further comprising: an insulating layer disposed over the substrate,wherein the insulating layer includes a third surface that follows thefirst surface contour of the curved region to provide a curvedinsulating layer within the curved region; wherein the conformalgraphene layer is disposed over the insulating layer.
 5. The device ofclaim 1, wherein the substrate further includes a substantially planarregion disposed adjacent to and on either side of the curved region. 6.The device of claim 5, wherein the second surface of the conformalgraphene layer follows a second surface contour of the substantiallyplanar region to provide a substantially planar graphene layer adjacentto and on either side of the curved region.
 7. The device of claim 6,wherein the curved graphene layer includes semiconducting graphene, andwherein the substantially planar graphene layer includes metallicgraphene.
 8. The device of claim 1, wherein the curved region includesone of a concave region and a convex region.
 9. The device of claim 1,wherein the conformal graphene layer includes one of monolayer graphene,bilayer graphene, and multi-layer graphene.
 10. The device of claim 1,wherein the curved graphene layer includes a channel region of thedevice.
 11. The device of claim 1, further comprising: a top-gatedielectric layer formed over the curved graphene layer; and a top-gateelectrode formed over the top-gate dielectric layer.
 12. A device,comprising: a substrate including a first surface contour defined by afirst region and a second region adjacent to and on either side of thefirst region, wherein the first region includes a curved region andwherein the second region includes a substantially planar region; aninsulating layer formed over the first and second regions of thesubstrate, wherein the insulating layer includes a second surfacecontour that conforms to the first surface contour of the substrate; agraphene layer formed over the insulating layer, wherein the graphenelayer includes a third surface contour that conforms to the secondsurface contour of the insulating layer, wherein the graphene layer overthe first region includes a curved graphene layer, and wherein thegraphene layer over the second region includes a substantially planargraphene layer; and source and drain electrodes in contact with thegraphene layer in the second region.
 13. The device of claim 12, furthercomprising: a top-gate dielectric layer formed over the graphene layerin the first region; and a top-gate electrode formed over the top-gatedielectric layer.
 14. The device of claim 12, wherein the curved regionincludes one of a concave region and a convex region.
 15. The device ofclaim 12, wherein the graphene layer includes one of monolayer graphene,bilayer graphene, and multi-layer graphene.
 16. The device of claim 12,wherein the first region includes a channel region of the device. 17.The device of claim 16, wherein the graphene layer is semiconductingwithin the channel region, and wherein the graphene layer is metallicbeneath the source and drain electrodes.
 18. A semiconductor device,comprising: a substrate including a nanorod, wherein the nanorodincludes an insulating outer surface that traverses a circumference ofthe nanorod; and a carbon nanotube (CNT) disposed on the insulatingouter surface of the nanorod; wherein the nanorod includes a firstdiameter, wherein the CNT includes a second diameter substantially equalto the first diameter, and wherein a CNT band gap is determined at leastin part by the first diameter.
 19. The semiconductor device of claim 18,wherein the CNT includes one of a single-wall CNT (SW-CNT), adouble-wall CNT (DW-CNT), and a multi-wall CNT (MW-CNT).
 20. Thesemiconductor device of claim 18, wherein the nanorod includes ametallic nanorod, a semiconducting nanorod, or an insulating nanorod.